Clare Hollingworth was 27 when she became a journalist – like much else in her life, thanks to a mixture of ferocious determination and barely credible luck. Having run into the editor of the Daily Telegraph in the last week of August 1939, she persuaded him to hire her and send her, the next day, to Poland. A few days later, she was returning across the border after a trip into Germany to buy supplies, when she noticed that large hessian screens had been erected on either side of the road. As she drove past, one of the screens flapped back in the wind to reveal hundreds of German tanks lined up and facing Poland. She had stumbled across the scoop of the century – the beginning of the second world war.

On Monday, Hollingworth turned 100 and, fittingly for one of the most legendary war reporters of the 20th century, the occasion was marked in style at the Foreign Correspondents' Club in Hong Kong, the expat watering hole of which she has been the doyenne for more than two decades. About 150 guests, including the consul general, attended, William Hague sent a congratulatory message, and guests were shown a film of Hollingworth's more-staggering-than-fiction career.

It will have been quite a movie. Having spent the war dashing around eastern and southern Europe, dodging German fighters on the Mediterranean and following Eisenhower's troops around north Africa armed only with what she called "a T and T" — typewriter and toothbrush — Hollingworth settled in Cairo with her second husband, where their neighbours — another stroke of luck, this — were Donald and Melinda Maclean. Through them she met Kim Philby and in 1963, after Hollingworth moved to the Guardian, it was she who uncovered the story of Philby's defection to the USSR as the "third man" (Maclean himself had defected in 1951).

Claire Hollingworth in 1966, on her return from Saigon. Photograph: Guardian

After a career-defining period covering the Algerian war in the 1950s and 1960s and a stint in Vietnam, Hollingworth moved to China for the Daily Telegraph in the early 70s, then a terrifyingly repressive and closed society. Typically, she loved it. She officially retired from the paper in 1980, aged 70, though she never considered herself to have stopped work.

I interviewed Hollingworth in Hong Kong in 2003, when she was 92 and already almost blind. Her mind, though, remained sharp, and she had only recently given up her habit of sleeping periodically on the floor to ensure she didn't "go soft". A suspected stroke a few years ago has left her more frail, though, with the help of her nurse, she spends part of most days at the FCC listening to foreign news broadcasts on the BBC.

Her great nephew Patrick Garrett was in Hong Kong yesterday to help her celebrate. Struggling to be heard over the congratulatory buzz, he said she, though more forgetful than she once was, "still enjoys a party" – Monday's was the second to mark her centenary.

Having met her, I said, I imagined she still considered herself to be on call should a story break out in the region. "Oh, she still sleeps with her passport beside her bed," said Garrett. "I don't think that will ever change."